Illumination device using coherent light source

ABSTRACT

The invention provides a structurally simple illumination device capable of safely illuminating the desired area with coherent light. An illumination device (1) includes a laser light source (11) (coherent light source), a light diffuser (14), and a light scanning device (21). The laser light source (11) emits laser beam L (coherent light). The light diffuser (14) diffuses the laser beam L emitted from the laser light source (11). The light scanning device (21) guides the laser beam L to one of the illumination subareas constituting part of an illumination area, thereby scanning the laser beam L radiated from the light diffuser (14) across the illumination area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/757,675, filed on Mar. 6, 2018 now U.S. Pat. No. 10,941,915, which,in turn, is a national phase entry of PCT Application No.PCT/JP2016/076303, filed on Sep. 7, 2016, which claims the priority fromJapanese Patent Application No. 2015-175871, filed on Sep. 7, 2015, andJapanese Patent Application No. 2016-092704, filed on May 2, 2016 in theJapanese Patent Office, the entire contents of which are herebyincorporated by reference into this application.

TECHNICAL FIELD

The present invention relates to an illumination device for illuminatinga predetermined range with coherent light.

BACKGROUND ART

Laser light sources have longer life spans and consume less power thanhigh-pressure mercury lamps, and their associated optical systems can bereduced in size. Thus, illumination devices using laser light sourcesare being widely used.

Patent Document 1 discloses a vehicle light capable of using a laseroscillator as a light source. The vehicle light includes a hologramelement. Stored on this hologram element is a hologram patterncalculated such that diffracted light regenerated by irradiating thehologram element with reference light forms a light distribution patternof a given light intensity distribution.

CITATION LIST Patent Literature

Patent Document 1: JP-A-2012-146621

SUMMARY OF INVENTION Technical Problem

By combining an optical element such as a hologram element with a laserlight source as in the above for use, the desired area can be irradiatedwith coherent light such as laser beam. Illumination devices usingcoherent light can be applied to devices in various fields. For example,they can be used for vehicle headlights.

Meanwhile, there is a demand for sectioning an illumination area intomany illumination subareas to achieve fine illumination of theillumination area or for illuminating part of or the entire illuminationarea by the densely packed illumination subareas. However, in a systemcombining a hologram element and a laser light source, generally, as thenumber of illumination subareas increases, the number of hologramelements needs to be increased. Thus, a preferred system is one capableof safely irradiating densely packed illumination subareas with coherentlight using an illumination device having a structure not dependent onthe number of light diffusers such as holograms.

A laser light source capable of emitting coherent light is also capableof emitting a laser beam with a minute light-emitting area but with morepowerful energy compared with lamp light sources or LEDs (light emittingdiodes), and has advantages such that it can control the distribution ofthe light more finely, and transmit the light farther. However, thecoherent light from a laser light source, the etendue of which, or theproduct of the light emitting surface area (cross-sectional area of thelight beam) and the radiation angle (solid angle), is very small, hasthe chance of the light power density increasing locally. When suchcoherent light is applied to illumination devices such as vehicleheadlights that persons may look at directly, it is necessary to ensuresafety.

The invention has been contrived in view of the above, and an object ofthe invention is to provide a structurally simple illumination devicecapable of illuminating the desired area safely with coherent light.

Solution to Problem

One aspect of the invention is directed to an illumination devicecomprising: a coherent light source which emits coherent light; a lightdiffuser which diffuses the coherent light from the coherent lightsource; and a light scanning device which scans the coherent light fromthe light diffuser in an illumination area so as to guide the coherentlight to illumination subareas constituting parts of the illuminationarea.

According to this aspect, a desired illumination subarea can beilluminated safely with coherent light using a structurally simpleillumination device.

The illumination device may further comprise a control unit whichcontrols an incident timing of the coherent light to the light diffuseror a timing of illuminating the illumination area.

The illumination device may further comprise a timing control unit whichcontrols a timing of emitting the coherent light according to scanningof the coherent light performed by the light scanning device.

The light scanning device may include: an irradiation surface which isirradiated with the coherent light from the light diffuser and changes apath of the coherent light; and a scan drive unit which adjusts anarrangement of the irradiation surface, and wherein a diffusion angle ofthe coherent light diffused by the light diffuser is smaller than anangle of each of the illumination subareas relative to the irradiationsurface.

According to this aspect, ‘the diffusion angle of the coherent lightdiffused by the light diffuser’ is included in an appropriate range thatis based on ‘the angle of each of the illumination subareas relative tothe irradiation surface’.

The diffusion angle of the coherent light diffused by the light diffusermay be larger than 0.05° and smaller than 2°.

According to this aspect, the illumination subareas having broadness canbe illuminated appropriately while controlling the diffusion of thecoherent light by the light diffuser to a proper range. Thus, it is notnecessary to provide an optical element for reducing the diffusion angleof the coherent light increased by the light diffuser, which leads to astructurally simple and compact illumination device.

The angle of each of the illumination subareas relative to theirradiation surface of the light scanning device may be larger than 0.1°and smaller than 5°.

According to this aspect, the illumination subareas can be irradiatedappropriately with the coherent light whose diffusion angle iscontrolled to a proper range by the light diffuser.

The light scanning device may be disposed at a position that is based onan imaging position of the coherent light from the light diffuser.

The light scanning device can be disposed at the position that agreeswith the position of the imaging position of the coherent light from thelight diffuser or can be disposed near the imaging position. When thelight scanning device is disposed at the position that agrees with theposition of the imaging position of the coherent light from the lightdiffuser, the light diffuser can be regarded as being disposed at theposition of the light scanning device.

The light diffuser may be a hologram.

The light diffuser may be a micro-lens array.

According to this aspect, the diffusion of the coherent light by thelight diffuser can be controlled with ease to a proper range.

The illumination device may further comprises a relay optical systemdisposed between the light diffuser and the light scanning device,wherein the coherent light from the light diffuser is guided to thelight scanning device through the relay optical system.

According to this aspect, the arrangement position of the light scanningdevice and the irradiation area irradiated with the coherent light canbe controlled by the relay optical system, and the above illuminationdevice can be applied flexibly to various types of light scanningdevices.

The illumination device may further comprise a beam expander which isdisposed between the coherent light source and the light diffuser andexpands a diameter of the coherent light from the coherent light source.

According to this aspect, the light entrance area of the coherent lightfor the light diffuser can be optimized by the beam expander.

The illumination device may further comprise a collimating opticalsystem which is disposed between the beam expander and the lightdiffuser and collimates the coherent light from the beam expander.

According to this aspect, the diffusion of the coherent light by thelight diffuser can be controlled with ease to a proper range.

A plurality of the coherent light sources which emit coherent lightshaving mutually different wavelengths may be provided, a plurality ofthe light diffusers which are correspondingly provided for the coherentlight sources respectively may be provided and each diffuse the coherentlight from corresponding one of the coherent light sources, and theillumination device may further comprise an optical guide unit whichguides to the light scanning device the coherent lights having mutuallydifferent wavelengths from the plurality of light diffusers.

The optical guide unit may include: a first optical guide memberdisposed between one light diffuser of the plurality of light diffusersand the light scanning device; and a second optical guide member whichguides to the first optical guide member the coherent light from anotherlight diffuser of the plurality of light diffusers, and wherein thefirst optical guide member guides to the light scanning device thecoherent light from the one light diffuser and the coherent light fromthe another light diffuser.

A plurality of the coherent light sources which emit coherent lightshaving mutually different wavelengths may be provided, and theillumination device may further comprise an optical guide unit whichguides to the light diffuser the coherent lights having mutuallydifferent wavelengths from the plurality of coherent light sources.

The optical guide unit may include: a first optical guide memberdisposed between one coherent light source of the plurality of coherentlight sources and the light diffuser; and a second optical guide memberwhich guides to the first optical guide member the coherent light fromanother coherent light source of the plurality of coherent lightsources, and wherein the first optical guide member guides to the lightdiffuser the coherent light from the one coherent light source and thecoherent light from the another coherent light source.

The illumination device may further comprise a plurality of collimatingoptical systems which are correspondingly provided for the plurality ofcoherent light sources respectively, each of the collimating opticalsystems collimating the coherent light from corresponding one of thecoherent light sources, wherein the optical guide unit guides to thelight diffuser the coherent lights which have been emitted from theplurality of coherent light sources and have passed through theplurality of collimating optical systems, the coherent lights havingmutually different wavelengths.

The illumination device may further comprises a collimating opticalsystem which collimates the coherent lights having mutually differentwavelengths, wherein the optical guide unit emits the coherent lightshaving mutually different wavelengths from the plurality of coherentlight sources toward the collimating optical system, so as to guide thecoherent lights to the light diffuser.

The illumination device may further comprises a beam expander whichexpands diameters of the coherent lights, wherein the optical guide unitguides the coherent lights having mutually different wavelengths fromthe plurality of coherent light sources to the light diffuser via thebeam expander and the collimating optical system.

Another aspect of the invention is directed to an illumination devicecomprising: a coherent light source which emits coherent light; a lightscanning device which changes a propagation direction of the coherentlight from the coherent light source; and a light diffuser whichdiffuses the coherent light from the light scanning device, wherein thelight scanning device scans the coherent light having passed through thelight diffuser in an illumination area so as to guide the coherent lightto illumination subareas constituting parts of the illumination area.

The coherent light which is changed in the propagation direction by thelight scanning device may have light components having mutuallydifferent wavelengths, a spectroscopic unit may be provided between thelight scanning device and the light diffuser, the coherent light fromthe light scanning device may be incident on the light diffuser via thespectroscopic unit, and the spectroscopic unit may spectrally dispersethe coherent light from the light scanning device into a plurality oflight components having wavelengths different from each other and emitsthe plurality of light components toward the light diffuser.

The spectroscopic unit may include: a first spectroscopic guide memberwhich allows a light component in a first wavelength range to passtherethrough and guide the light component to the light diffuser, whilereflecting light components in other wavelength ranges; and a secondspectroscopic guide member which guides the light components in theother wavelength ranges reflected by the first spectroscopic guidemember to the light diffuser.

Advantageous Effects of the Invention

According to the invention, a structurally simple illumination devicecan be achieved. In addition, a desired area can be illuminated safelywith coherent light.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an outline of a structure ofan illumination device according to Embodiment 1 of the invention;

FIG. 2 is a block diagram illustrating an example of a functionalstructure of a controller;

FIG. 3 is a conceptual diagram illustrating an illumination area of alaser beam guided by a light scanning device;

FIG. 4 is a conceptual diagram illustrating an outline of a structure ofan illumination device according to Modification 1;

FIG. 5 is a diagram illustrating an example of arrangement of areflective mirror of the modification of FIG. 4 and an irradiationsurface (light scanning device) and shows an configuration example in acase where laser beams are reflected vertically by the reflectivemirror;

FIG. 6 is a diagram illustrating an example of arrangement of thereflective mirror of the modification of FIG. 4 and the irradiationsurface (light scanning device) and shows an configuration example in acase where laser beams are reflected horizontally (laterally) by thereflective mirror;

FIG. 7 is a conceptual diagram illustrating an outline of a structure ofan illumination device according to Modification 2;

FIG. 8 is a conceptual diagram illustrating an outline of a structure ofan illumination device according to Modification 3;

FIG. 9 is a conceptual diagram illustrating an outline of a structure ofan illumination device according to Embodiment 2 of the invention;

FIG. 10 is a conceptual diagram illustrating an outline of a structureof an illumination device according to Embodiment 3 of the invention;

FIG. 11 is a conceptual diagram illustrating an outline of a structureof an illumination device according to Embodiment 4 of the invention;

FIG. 12 is a conceptual diagram illustrating an outline of a structureof an illumination device according to Embodiment 5 of the invention;and

FIG. 13 is a conceptual diagram illustrating an outline of a structureof an illumination device according to Embodiment 6 of the invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings. In the drawings appended to thespecification, for illustration and clarification purposes, the actualscales or proportions of dimensions are changed or exaggerated.

In this specification, words that specifies shapes, geometricconditions, or the degrees of such traits, such as words like‘parallel,’ ‘perpendicular,’ and ‘identical’ and the values of lengthsand angles, are to be interpreted not in their strict meanings but toinclude ranges that would achieve similar functions.

Embodiment 1

FIG. 1 is a conceptual diagram illustrating an outline of a structure ofan illumination device 1 according to Embodiment 1 of the invention.

The illumination device 1 of the present embodiment includes a laserlight source 11, a beam expander 12, a collimating optical system 13, alight diffuser 14, a relay optical system 18, and a light scanningdevice 21.

The laser light source 11 is a source of laser beams, that is, coherentlight L. Typically, the laser light source 11 is a semiconductor laserlight source. The laser light source 11 can consist of one or more lightsources. When the laser light source 11 consists of multiple lightsources, the spectrums of the laser beams L emitted from the lightsources can be the same or different. To increase the illuminationintensity of the laser beam L emitted from the laser light source 11, itis preferred that the spectrums of the laser beams L emitted frommultiple light sources overlap one another. When the laser beams Lemitted from the multiple light sources constituting the laser lightsource 11 have different spectrums, the multiple light sources can beprovided independently of one another or arranged on a common substrateto form a light source module. For example, when the multiple lightsources constituting the laser light source 11 are capable of emittinglaser beams L with red, green, and blue spectrums, overlapping the threelaser beams L results in white illumination light.

The laser light source 11 can include a light emission control unit (notillustrated) for controlling the emission of laser beam. The lightemission control unit is controlled by a light emission timing controlunit 25, described later. The light emission control unit can, forexample, separately control the timings of emitting laser beams havingdifferent spectrums. In other words, when multiple light sources areprovided to produce laser beams with different spectrums, the lightemission control unit can control for each light source the timings atwhich laser beams are emitted from the multiple light sources. Thus,when the laser light source 11 is capable of emitting red, green, andblue laser beams, controlling the timings of emitting the laser beamsproduces a red, green, or blue light or lights of mixed colors obtainedby mixing two or more of the colors. The light emission control unit canalso control the emission intensities of the laser beams from the lightsources, thereby emitting a high or low intensity laser beam from eachof the light sources.

The beam expander 12 is disposed between the laser light source 11 andthe light diffuser 14. In the present embodiment, it is disposed betweenthe laser light source 11 and the collimating optical system 13 toexpand the diameter of the laser beam L from the laser light source 11.The collimating optical system 13 is disposed between the beam expander12 and the light diffuser 14 to collimate the light from the beamexpander 12. Thus, the small-diameter laser beam L emitted from thelaser light source 11 is expanded in diameter by the beam expander 12and collimated by the collimating optical system 13, thereby beingoptimized for the size of the input section of the later-stage lightdiffuser 14 before entering the light diffuser 14. In FIG. 1, forillustration and clarification purposes, the laser beam L is notillustrated in the section from the collimating optical system 13 to thelight scanning device 21.

The light diffuser 14 consists of multiple diffuser elements 15 anddiffuses the laser beam L from the laser light source 11. As will bedescribed later in detail, in the present embodiment, it is preferredthat the light diffuser 14 be a high-directivity optical element capableof diffusing the laser beam L at a relatively gentle angle. Such a lightdiffuser 14 element is typically a micro-lens array; in that case, themicro-lenses that form the array each constitute one of the diffusingelements 15. The light diffuser 14 can also be a hologram recordingmedium. Specifically, examples of hologram recording media includecomputer generated holograms (CGH) and Fourier transform holograms.Further examples include volume hologram recording media usingphotopolymers, volume hologram recording media that are photosensitivemedia including silver halide materials, and relief (embossed) hologramrecording media.

The structure and effects of the light diffuser 14 are described laterin detail.

The relay optical system 18 is disposed between the light diffuser 14and the light scanning device 21. In the present embodiment, the relayoptical system 18 includes a first relay lens 16 and a second relay lens17. The laser beam L from the light diffuser 14 is guided through therelay optical system 18 to the light scanning device 21, whereby animage is formed on an irradiation surface 19 of the light scanningdevice 21. In the present embodiment, the image of the light diffuser14, that is, the image of a virtual micro-lens array 31, is formed onthe irradiation surface 19 of the light scanning device 21. The virtualmicro-lens array 31 formed on the irradiation surface 19 of the lightscanning device 21 can be treated as a virtual light source; in thatcase, it follows that, as illustrated in FIG. 3, the laser beam L fromthe virtual micro-lens array 31 irradiates the individual illuminationsubareas 41 included in an entire illumination area 40.

The relay optical system 18 is not limited to particular structures. Bycontrolling the optical characteristics of the optical elementsconstituting the relay optical system 18, that is, adjusting the focaldistances of the first relay lens 16 and the second relay lens 17, therelay optical system 18 can be made to function as an unmagnificationoptical system, magnification optical system, or de-magnificationoptical system. For example, by forming the relay optical system 18using a first relay lens 16 and a second relay lens 17 with the samefocal distances, the optical magnification of the relay optical system18 can be set to 1 (unmagnification). On the other hand, by forming therelay optical system 18 using a first relay lens 16 and a second relaylens 17 with different focal distances, the optical magnification of therelay optical system 18 can be changed (magnification orde-magnification) according to the ratio of the focal distances of thetwo lenses. As above, by making the relay optical system 18 an afocalsystem, it is double telecentric, which fixes the height of an imageformed on the light emission side. As a result, the influence of theirradiation area of the light diffuser 14 on the illumination area in adistant field of view becomes considerably small, and highly preciseillumination can be performed. It is to be noted that when the relayoptical system 18 is a de-magnification optical system, the diffusionangle of the laser beam L diffused from the light scanning device 21becomes relatively large. When the relay optical system 18 is amagnification optical system, the diffusion angle of the laser beam Ldiffused from the light scanning device 21 becomes relatively small.

In the present embodiment, as will be described later in detail, byirradiating the irradiation surface 19 of the light scanning device 21with the laser beam L passing through the light diffuser 14, theindividual illumination subareas 41 included in the entire illuminationarea 40 are illuminated with the laser beam L. Thus, by adjusting withthe relay optical system 18 ‘the irradiation range (irradiation area) ofthe irradiation surface 19 of the light scanning device 21,’ irradiatedwith the laser beam L from the light diffuser 14, the appropriate range(area) of the irradiation surface 19 is irradiated with the laser beamL.

The light scanning device 21 includes the irradiation surface 19irradiated with the laser beam L from the light diffuser 14 and a scandrive unit 20 that adjusts the arrangement of the irradiation surface19. As illustrated in FIG. 3, the laser beam L from the light diffuser14 is scanned across the illumination area 40 to guide the laser beam Lto the individual illumination subareas 41 that constitute part of theillumination area. In other words, the irradiation surface 19 changesthe path of the laser beam L radiated and guides the light L to theindividual illumination subareas 41 included in the entire illuminationarea 40. The scan drive unit 20 is connected to a controller 22.Controlled by the controller 22, the scan drive unit 20 adjusts thefacing direction of the irradiation surface 19, thereby changing theindividual illumination subareas 41 in the illumination area 40 to beirradiated with the laser beam L. The irradiation surface 19 can be amirror, examples of which include a MEMS (micro electro mechanicalsystems) mirror such as a polygon mirror, a two-shaft galvanometermirror, and a resonance mirror and a two-shaft large-diameter resonancemirror with a reflective surface of several tens of millimeters (mm)diameter.

Instead of using the above light scanning device with a mirror, it isalso possible to scan the laser beam by making oscillate a lighttransparent member such as a lens, an example of which is a Fresnellens. When a laser beam is incident on a Fresnel lens, it passes throughthe lens and is then scanned across the irradiation area. When the lightscanning device uses a Fresnel lens, the laser beam emission surface ofthe lens serves as the irradiation surface 19.

The light scanning device 21, especially the irradiation surface 19, isdisposed at the position that is based on the imaging position of thelaser beam L passing through the light diffuser 14. As stated above, inthe present embodiment, the laser beam L emitted through the individualdiffusing elements 15 of the light diffuser 14 irradiates theirradiation surface 19 of the light scanning device 21 through the relayoptical system 18. Thus, in the present embodiment, the arrangementposition of the light scanning device 21 is determined based on theimaging position determined in accordance with the opticalcharacteristics (focal distances) of the individual diffusing elements15 of the light diffuser 14 and the optical characteristics (focaldistance) of the relay optical system 18. When the relay optical system18 is not provided, the arrangement position of the irradiation surface19 of the light scanning surface 21 is preferably determined based onthe imaging position determined in accordance with the opticalcharacteristics (focal distances) of the individual diffusing elements15 of the light diffuser 14.

The phrase ‘the position that is based on the imaging position of thelaser beam L passing through the light diffuser 14’ used hereintypically refers to the position that agrees with the imaging position,but they do not necessarily need to precisely agree with each other.Instead, the irradiation surface 19 of the light scanning device 21 canalso be disposed near an area in which the influence on imagingperformance can be tolerated, for example, near ‘the imaging position ofthe laser beam L passing through the light diffuser 14.’

The controller 22 is connected to the laser light source 11 and thelight scanning device 21, especially the scan drive unit 20 of the lightscanning device 21, and performs on/off control for the emission of thelaser beam L from the laser light source 11 and control for the scanningof the laser beam L by the irradiation surface 19 of the light scanningdevice 21. In place of the on/off control for the light emission fromthe laser light source 11, it is also possible to provide a lightshutting section, not illustrated, between the laser light source 11 andthe light diffuser 14 and use the light shutting section to permit ornot to permit the emission of the laser light source. In either case,the controller 22 controls the timing of the laser beam incident on thelight diffuser 14 and the timing of illuminating the illumination area.

FIG. 2 is a block diagram illustrating a functional structure of thecontroller 22. The controller 22 includes the light emission timingcontrol unit 25 for controlling the laser light source 11 and an opticalscan control unit 26 for controlling the scan drive unit 20 of the lightscanning device 21.

In cooperation with the an optical scan control unit 26, the lightemission timing control unit 25 of the present embodiment controls thetiming of the emission of the laser beam L based on the scanning of thelaser beam L by the light scanning device 21. This allows, asillustrated in FIG. 3, only part of the areas within the entireillumination area 40 to be or not to be illuminated with the laser beamL.

FIG. 3 is a conceptual diagram illustrating the illumination area 40illuminated with the laser beam L guided by the light scanning device21.

In the present embodiment, the laser beam L guided by the light scanningdevice 21 irradiates the individual illumination subareas 41constituting part of the illumination area 40. In other words, only oneillumination subarea 41 within the illumination area 40 is illuminatedwith the laser beam L from the laser scanning device 21 at a time. Whenthe entire illumination area 40 is illuminated, the light scanningdevice 21 scans the laser beam L at high speed within the illuminationarea 40. The method of scanning the laser beam L by the light scanningdevice 21 is not particularly limited. For example, it is possible toadopt the raster scan method as illustrated by ‘S’ in FIG. 3, theLissajous scan method, or the vector scan method.

How to section the illumination area 40 into the illumination subareas41 is not also limited. The range that can be illuminated at a time isdetermined as an individual illumination subarea 41 by the laser beam Lfrom the light scanning device 21. For this reason, each illuminationsubarea 41 is determined based on the timing of emitting the laser beamL from the laser light source 11, which is controlled by the controller22, and on the scan position of the laser beam L scanned by the lightscanning device 21. Therefore, as illustrated in FIG. 3, it is possibleto set the illumination subareas 41 such that they overlap or do notoverlap one another or create in the illumination area 40 areas in whichsome of the individual illumination subareas 41 overlap and areas inwhich some of the individual illumination subareas 41 do not overlap.

The illumination subareas 41 illuminated with the laser beam L from thelight scanning device 21 expand gradually according to the diffusionangle of the laser beam L as they are located farther away from thelight scanning device 21. For this reason, the individual illuminationsubareas 41 constituting the illumination area illuminated by theillumination device 1 are wider at a position located relatively faraway from the light scanning device 21 (far field) than at a positionrelatively close to the light scanning device 21 (near field). Thus, itis often convenient to represent the sizes of the individualillumination subareas by their angular distributions in angular spacethan by their actual dimensions. The word ‘illumination area’ usedherein also includes their angular ranges in angular space as well asthe actual irradiation area irradiated with the laser beam L and theactual illumination ranges.

The structure and effects of the light diffuser 14 of FIG. 1 isdescribed below in detail.

The individual diffusing elements 15 constituting the light diffuser 14serve as virtual light sources for the laser beams L emitted in adiffused manner from the light diffuser 14. In other words, the laserbeams L emitted from the light diffuser 14 can be regarded as beingemitted from the virtual light sources.

Generally, when the irradiation intensities of the laser beams Ldemanded for the illumination area (individual illumination subareas)are the same, the laser beams L emitted from multiple light sourcesrequire less light power density and thus safer than the laser beam Lemitted from a single light source. In other words, when the sameirradiation intensity is required for the laser beam L, directly lookingat the laser beams L emitted from multiple light sources with the humaneyes has less influence on the eyes when the images of the light sourcesare formed on the retinas than directly looking at the laser beam Lemitted from a single light source. Therefore, as in the presentembodiment, by providing the light diffuser 14 including the individualdiffusing elements 15 at a stage subsequent to the laser light source11, the individual illumination subareas 41 constituting theillumination area can be illuminated safely with the laser beam Lpassing through the light diffuser 14.

As a property of light in an optical system, the law of etenduegenerally holds true. The law of etendue states that the product of thecross-sectional area (light-emitting area) of a light beam and the solidangle (radiation angle) of its diffused light is maintained at aconstant value, and etendue indicates how spread out the light is inarea and angle. When the light diffuser 14 is placed on the path of thelaser beam L as in the present embodiment, the law of etendue applies tothe downstream side of the light diffuser 14 in terms of the propagationdirection of the laser beam L, with the ‘apparent light source’ formedby the light diffuser 14 being used as a reference.

The diffusion angle of the laser beam L diffused by the light diffuser14 is smaller than the angular space range of an illumination subarea41, that is, the angle of an illumination subarea 41 with respect to theirradiation surface 19 of the light scanning device 21.

As stated above, from a safety point of view, the larger the area of thelight source is, the better it is. However, to reduce the sizes of theindividual illumination subareas 41 when the laser beam L is emittedfrom a light source with a large light-emitting area, thecross-sectional area of the laser beam L needs to be reduced. Accordingto the law of etendue, however, the diffusion angle of the laser beam Lincreases when the cross-sectional area of the laser beam L decreases,which means that it becomes difficult to illuminate a wide area atproper light intensity. In other words, as the diffusion angle of thelaser beam L increases, the optical mechanism that adjusts the diffusionangle of the laser beam L necessary to illuminate the space-limitedillumination subareas 41 needs to be larger in size and more complex.Also, to illuminate a wide range with proper light intensity in thepropagation direction of the laser beam L guided by the light scanningdevice 21, it is preferred that the diffusion angle of the laser beam Ldiffused by the light diffuser 14 that forms the apparent light sourcebe small. Thus, to illuminate a wide portion of each of thespace-limited illumination subareas 41 at proper light intensity, it ispreferred that the diffusion angle of the laser beam L diffused by thelight diffuser 14 be within an appropriate angular range. Such anappropriate angular range is determined by the angular ranges of theindividual illumination subareas 41.

Specifically, the diffusion angle of the laser beam L diffused by thelight diffuser 14 is preferably larger than 0.05° and smaller than 2°.‘The diffusion angle of the laser beam L diffused by the light diffuser14 of the present embodiment’ is determined by the diffusion angles ofthe laser beams L diffused by the individual diffusing elements 15constituting the light diffuser 14, and each of the diffusing elements15 preferably has a diffusion angle of larger than 0.05° but smallerthan 2°. It is also preferred that the angle of each of the illuminationsubareas 41 relative to the irradiation surface 19 of the light scanningdevice 21 be larger than 0.1° and smaller than 5°. When the diffusionangle of the laser beam L diffused by the light diffuser 14 and theangular range of each of the illumination subareas 41 are within thoseranges, a wide portion of each of the illumination subareas 41 can beilluminated at proper light intensity.

‘The diffusion angle of the laser beam L diffused by the light diffuser14’ is measured by irradiating the light diffuser 14 with the laser beamL and is the angle of the collimated laser beam L diffused by the lightdiffuser 14. ‘The angle of each of the illumination subareas 41 relativeto the irradiation surface 19 of the light scanning device 21 (theangular range of each of the illumination subareas 41)’ is the angleformed by lines connecting a representative point on the irradiationsurface 19 of the light scanning device 21 and representative positionsof the illumination subareas 41; for example, it is the angle formed bylines connecting one or more representative points on the irradiationsurface 19 and two or more representative positions of the illuminationsubareas 41.

As described above, according to the illumination device 1 of thepresent embodiment, at the light diffuser 14 having a light diffusionangle within a predetermined range and the illumination area 40,illumination of the illumination subareas 41 by the laser beam L isperformed by the scan light scanning device 21 that scans the laser beamL. With this, the illumination device 1 capable of safely illuminatingthe individual illumination subareas 41 within the illumination area 40using the laser beam L can be realized. Moreover, a structurally simpleillumination device that does not involve complex and costly devices canbe achieved.

<Modification 1>

FIG. 4 is a conceptual diagram illustrating an outline of a structure ofan illumination device 1 according to modification 1 of the illuminationdevice 1 of FIG. 1. In this modification, a reflective mirror 45 isprovided between the second relay lens 17 of the relay optical system 18and particularly the irradiation surface 19 of the light scanning device21. The rest is the same as in the above-described illumination device 1of FIG. 1.

The reflective mirror 45 reflects the laser beam L from the second relaylens 17 of the relay optical system 18 and guides the reflected laserbeam L to particularly the irradiation surface 19 of the light scanningdevice 21. With the use of the reflective mirror 45, the propagationdirection of the laser beam L can be changed to the desired direction,and the path of the laser beam L can be optimized flexibly based onspatial demand such as for installation space. Thus, it is possible toarrange the optical systems in a more compact manner when the reflectivemirror 45 is used to adjust the laser beam L as in the presentmodification than when, as with the illumination device 1 of FIG. 1, theoptical axis of the laser beam L is bent at a relatively large anglesuch as at a right angle by the irradiation surface 19 of the lightscanning device 21.

The specific structure of the reflective mirror 45 is not particularlylimited, and a plane mirror can be used to form the reflective mirror45. Alternatively, a concave mirror can be used to form the reflectivemirror 45, or the reflective mirror 45 can be provided as part of therelay optical system 18. Also, the reflection direction of the laserbeam L by the reflective mirror 45 is not particularly limited.

FIGS. 5 and 6 are diagrams illustrating examples of arrangement of thereflective mirror 45 of the modification of FIG. 4 and the irradiationsurface 19 of the light scanning device 21 and are diagrams of thereflective mirror 45 and the irradiation surface 19 as viewed from afront direction (see the arrow ‘X’ of FIG. 4). FIG. 5 illustrates a casewhere the laser beam L is reflected vertically by the reflective mirror45 while FIG. 6 illustrates a case where the laser beam L is reflectedhorizontally (laterally) by the reflective mirror 45. The direction inwhich the reflective mirror 45 reflects the laser beam L is notparticularly limited, and the reflective mirror 45 can guide the laserbeam L in any desired direction. Also, multiple reflective mirrors 45can be provided, and the reflective mirrors 45 capable of reflecting thelaser beam L in different directions can be provided between the secondrelay lens 17 of the relay optical system 18 and the irradiation surface19 of the light scanning device 21.

<Modification 2>

FIG. 7 is a conceptual diagram illustrating the structure of anillumination device 1 according to Modification 2 of the illuminationdevice 1 of FIG. 1. In this modification, in place of the beam expander12, an optical fiber 48 is provided between the laser light source 11and the collimating optical system 13. The rest is the same as in theillumination device 1 of FIG. 1.

In this modification, the laser beam L emitted from the laser lightsource 11 travels from the laser light source 11 directly into theoptical fiber 48, and the laser beam L is emitted from the optical fiber48 toward the collimating optical system 13. The laser beam L emittedfrom the optical fiber 48 is incident on the collimating optical system13 in a diffused manner, where it is collimated by the collimatingoptical system 13.

In this structure, as the diameter of the laser beam L collimated by thecollimating optical system 13 is increased relative to the core diameterof the optical fiber 48 (the diameter of the path of the laser beam L),the laser beam L can be collimated more accurately, and the degree ofthe parallelness of the laser beam L can be increased.

<Modification 3>

FIG. 8 is a conceptual diagram illustrating an outline of a structure ofan illumination device 1 according to Modification 3 of the illuminationdevice 1 of FIG. 1. In this modification, multiple laser light sources11 are provided, and multiple collimating optical systems 13 areprovided. Also, in place of the beam expander 12, multiple opticalfibers 48 are provided between the laser light sources 11 and thecollimating optical systems 13. The rest is the same as in the abovedescribed illumination device 1 of FIG. 1.

In this medication, one of the optical fibers 48 and one of thecollimating optical systems 13 are allocated to each of the laser lightsources 11. The laser beams L emitted from the laser light sources 11travel from the laser light sources 11 directly into the associatedoptical fibers 48. Thereafter, the laser beams L are emitted from theoptical fibers 48 to the associated collimating optical systems 13. Inthis modification as well, similar to Modification 2, the laser beams Lemitted from the optical fibers 48 are incident on the collimatingoptical systems 13 in a diffused manner, where they are collimated bythe respective collimating optical systems 13.

By emitting the laser beams L emitted from the multiple laser lightsources 11 via the multiple optical fibers 48 as in the presentmodification, the core diameter of each optical fiber 48 can be reducedif the total output is constant. Thus, variations in the angles of thelaser beams L that have passed through the collimating optical systems13 (collimating optical system array), that is, the angles of thecollimated laser beams L, can be reduced, and the collimating opticalsystems 13 can emit laser beams L that are closer to parallel beams.

Embodiment 2

FIG. 9 is a conceptual diagram illustrating an outline of a structure ofan illumination device 1 according to Embodiment 2 of the invention. Inthis embodiment, the same reference characters are used to refer toelements that are the same as or similar to those used in Embodiment 1,and such elements will not be described further in detail. In FIG. 9,for illustration and clarification purposes, the laser beam L is notillustrated in the section from collimating optical systems 13 a, 13 b,and 13 c to the light scanning device 21.

In the present embodiment, a first laser light source 11 a, a secondlaser light source 11 b, and a third laser light source 11 c areprovided as multiple laser light sources. The first laser light sources11 a, the second laser light sources 11 b, and the third laser lightsource 11 c emit laser beams L with mutually different wavelengths.

As multiple light diffusers, a first light diffuser 14 a, a second lightdiffuser 14 b, and a third light diffuser 14 c are provided. The firstlight diffuser 14 a, the second light diffuser 14 b, and the third lightdiffuser 14 c are formed by holograms and provided for the first laserlight source 11 a, the second laser light source 11 b, and the thirdlaser light source 11 c, respectively, to diffuse the laser beams Ltherefrom.

The illumination device 1 further includes an optical guide unit 50 thatguides to the light scanning device 21 the laser beams L with mutuallydifferent wavelengths from the first light diffuser 14 a, the secondlight diffuser 14 b, and the third light diffuser 14 c. The opticalguide unit 50 includes a first optical guide member 51 and secondoptical guide members 52.

The first optical guide member 51 is disposed between one of the lightdiffusers 14 a to 14 c, in the case of FIG. 9, the first light diffuser14 a, and the light scanning device 21 and has a dichroic mirror. Thefirst optical guide member 51 having a dichroic mirror is also called adichroic cube and has the property of letting the laser beam L from thefirst light diffuser 14 a pass therethrough while reflecting the laserbeams L with the other wavelengths. The second optical guide members 52have mirrors guiding the laser beams L from the other light diffusers ofthe light diffuser 14 a to 14 c, or the second light diffuser 14 b andthe third light diffuser 14 c in FIG. 9, to the first optical guidemember 51. The first optical guide member 51 guides via the relayoptical system 18 to the light scanning device 21 the laser beam L fromthe first light diffuser 14 a and the laser beams L from the secondlight diffuser 14 b and the third light diffuser 14 c via the secondoptical guide members 52.

Multiple beam expanders and multiple collimating optical systems arealso provided. A first beam expander 12 a and a first collimatingoptical system 13 a are provided between the first laser light source 11a and the first light diffuser 14 a. A second beam expander 12 b and asecond collimating optical system 13 b are provided between the secondlaser light source 11 b and the second light diffuser 14 b. A third beamexpander 12 c and a third collimating optical system 13 c are providedbetween the third laser light source 11 c and the third light diffuser14 c. The collimating optical systems 13 a to 13 c correspondinglyprovided for the laser light sources 11 a to 11 c, are used to collimatethe laser beams L from the laser light sources.

The light diffusers 14 a to 14 c each have a light diffusing propertysuitable for the wavelength of the laser beam L from the correspondinglaser light sources 11 a to 11 c, and the diffusion angles of the laserbeams L with different wavelengths are matched by the light diffusers 14a to 14 c. Thereafter, the laser beams L with respective wavelengths aresynthesized by the first optical guide member 51 and the second opticalguide members 52 and guided via the relay optical system 18 to the lightscanning device 21. The irradiation surface 19 of the light scanningdevice 21 is placed at the position that is based on the imagingposition of the laser beams L from the light diffusers 14 a to 14 c. Thecontroller 22 controls the timings of emitting the laser beams L fromthe laser light sources in cooperation with the scan control by thelight scanning device 21.

According to the above-described illumination device 1, any desiredillumination subarea 41 of the illumination area 40 can be illuminatedsafely with the laser beams of different wavelengths. Thus, by emittinglaser beams L of red-color, green-color, and blue-color wavelengths fromthe laser light sources 11 a to 11 c, the illumination area 40 can beilluminated with full color light.

Embodiment 3

FIG. 10 is a conceptual diagram illustrating an outline of a structureof an illumination device 1 according to Embodiment 3 of the invention.In this embodiment, the same reference characters are used to refer toelements that are the same as or similar to those used in Embodiment 2,and such elements will not be described further in detail. In FIG. 10,for illustration and clarification purposes, the laser beam L is notillustrated in the section from the collimating optical systems 13 a, 13b, and 13 c to the light scanning device 21.

In this embodiment, one light diffuser 14 is provided, and this lightdiffuser 14 is formed by a micro-lens array. The optical guide unit 50is arranged such that the laser beams L with mutually differentwavelengths from the laser light sources 11 a to 11 c are guided to thelight diffuser 14.

Specifically, the first optical guide member 51 having a dichroic mirroris disposed between one of the laser light sources, in the case of FIG.10, the laser light source 11 a, and the light diffuser 14. The secondoptical guide members 52 are arranged at the positions where the laserbeams L from the other light sources, in the case of FIG. 10, the secondlaser light source 11 b and the third laser light source 11 c, areguided to the first optical guide member 51. More specifically, thefirst optical guide member 51 is disposed between the first collimatingoptical system 13 a and the light diffuser 14. Also, the second opticalguide members 52 are disposed at the positions where the laser beams Lfrom the second collimating optical system 13 b and the thirdcollimating optical system 13 c are guided to the first optical guidemember 51. The first optical guide member 51 guides to the lightdiffuser 14 the laser beam L from the first laser light source 11 a andthe laser beams L from the second laser light source 11 b and the thirdlaser light source 11 c via the second optical guide members 52.

As described above, the optical guide unit 50 guides to the lightdiffuser 14 the laser beams L having mutually different wavelengthsemitted from the laser light sources 11 a to 11 c and passing throughthe beam expanders 12 a to 12 c and the collimating optical systems 13 ato 13 c.

In the present embodiment, the laser beams L from the laser lightsources 11 a to 11 c are synthesized at a stage prior to the lightdiffuser 14. The controller 22 controls the timings of emitting thelaser beams L from the laser light sources in cooperation with the scancontrol by the light scanning device 21.

Embodiment 4

FIG. 11 is a conceptual diagram illustrating an outline of a structureof an illumination device 1 according to Embodiment 4 of the invention.In this embodiment, the same reference characters are used to refer toelements that are the same as or similar to those used in Embodiment 3,and such elements will not be described further in detail. In FIG. 11,for illustration and clarification purposes, the laser beam L is notillustrated in the section from the laser light sources 11 a, 11 b, and11 c to the light scanning device 21.

In this embodiment, one beam expander 12 and one collimating opticalsystem 13 are provided, and the optical guide unit 50 is placed at astage prior to the beam expander 12. The first optical guide member 51is disposed between the first laser light source 11 a and the beamexpander 12. The second optical guide members 52 are disposed at thepositions where the laser beams L from the second laser light source 11b and the third laser light source 11 c are guided to the first opticalguide member 51. The first optical guide member 51 and the secondoptical guide members 52 synthesize the laser beams L from the laserlight sources 11 a to 11 c at a stage prior to the beam expander 12. Thesynthesized laser beam L is emitted from the first optical guide member51 to the beam expander 12.

As described above, the optical guide unit 50 emits the laser beams L ofmutually different wavelengths emitted from the laser light sources 11 ato 11 c to the beam expander 12 and the collimating optical system 13,thereby guiding them to the light diffuser 14. The collimating opticalsystem 13 is used to collimate the laser beams L of mutually differentwavelengths from the laser light sources 11 a to 11 c. The controller 22controls the timings of emitting the laser beams L from the laser lightsources in cooperation with the scan control by the light scanningdevice 21.

Embodiment 5

FIG. 12 is a conceptual diagram illustrating an outline of a structureof an illumination device 1 according to Embodiment 5 of the invention.In this embodiment, the same reference characters are used to refer toelements that are the same as or similar to those used in Embodiment 1,and such elements will not be described further in detail. In FIG. 12,for illustration and clarification purposes, the laser beam L isillustrated only in the section between the laser light source 11 andthe collimating optical system 13 and not illustrated in the othersections.

In this embodiment, the relay optical system 18 is removed, and thelight diffuser 14 is provided between the light scanning device 21 andthe illumination area 40. The light scanning device 21 is used to changethe propagation direction of the laser beam L travelling from the laserlight source 11 through the beam expander 12 and the collimating opticalsystem 13, and the light diffuser 14 is used to diffuse the laser beam Lfrom the light scanning device 21.

The laser beam L from the laser light source 11 is expanded in beamdiameter by the beam expander 12 and the collimating optical system 13and collimated before irradiating the light scanning device 21. Thelight scanning device 21 scans the laser beam L that has passed throughthe light diffuser 14 across the illumination area 40, thereby guidingthe laser beam L to one of the illumination subareas 41 constitutingpart of the illumination area 40.

Embodiment 6

FIG. 13 is a conceptual diagram illustrating an outline of a structureof an illumination device 1 according to Embodiment 6 of the invention.In this embodiment, the same reference characters are used to refer toelements that are the same as or similar to those used in Embodiment 5,and such elements will not be described further in detail. In FIG. 13,for illustration and clarification purposes, the laser beam L isillustrated only in the section between the laser light source 11 andthe collimating optical system 13 and not illustrated in the othersections.

In this embodiment, the laser beam L emitted from the laser light source11 and changed in direction by the light scanning device 21 includesmultiple light components having mutually different wavelengths. Aspectroscopic unit 60 is provided between the light scanning device 21and the light diffuser 14. The laser beam L from the light scanningdevice 21 is incident on the light diffuser 14 via the spectroscopicunit 60. The spectroscopic unit 60 spectrally disperses the laser beam Lincident on the spectroscopic unit 60 from the light scanning device 21or separates the laser beam L into multiple light components havingmutually different wavelengths, thereby emitting the light componentstoward the light diffuser 14.

The spectroscopic unit 60 of FIG. 13 includes a first spectroscopicguide member 61 and second spectroscopic guide members 62. The firstspectroscopic guide member 61 has a dichroic mirror for letting a lightcomponent having a first wavelength range pass therethrough to guide thelight component to the light diffuser 14 while reflecting the lightcomponents with the other wavelength ranges. The second optical guidemembers 62 guide to the light diffuser 14 the light components havingthe other wavelength ranges, reflected by the first spectroscopic guidemember 61. The light components having different wavelengths guided bythe first spectroscopic guide member 61 and the second spectroscopicguide members 62 are guided to different sections of the light diffuser14 and incident on the associated light diffusers 14 each formed by ahologram. Each of the light components is diffused by the associatedlight diffuser 14 to illuminate one of the illumination subareas 41within the illumination area 40.

For example, when the laser beam L emitted from the laser light source11 includes light components having red-color, green-color, andblue-color wavelength ranges, the laser beam L incident on thespectroscopic unit 60 is separated into those components havingrespective wavelength ranges. The light component having the red-colorwavelength range is guided by the spectroscopic unit 60 such that thelight component is incident on the light diffuser 14 optimized for it.Similarly, the light components having the green-color and blue-colorwavelength ranges are guided by the spectroscopic unit 60 such that theyare incident on the light diffusers 14 optimized for them. In thisembodiment as well, the controller 22 controls the timings of emittingthe laser beams L from the laser light sources in cooperation with thescan control by the light scanning device 21.

<Other Modifications>

The invention is not limited to the foregoing embodiments andmodifications, but allows other modifications.

For example, one or more elements selected from among the beam expander12, the collimating optical system 13, and the relay optical system 18can be removed, and the invention can also be applied to theillumination device 1 that does not include some of the elements ofFIG. 1. For instance, when the relay optical system 18 is not provided,it is possible to place the irradiation surface 19 of the light scanningdevice 21 near the light diffuser 14, for example, at a position locatedaway from the light diffuser 14 by the focal distance of the lightdiffuser 14 or near that position, and illuminate the illumination area40 with the laser beam L. Also, a condenser lens can be provided on theupstream side of the light scanning device 21, or on the side of thelaser light source, in addition to the relay optical system 18. Further,a condenser lens can also be provided on the downstream side of thelight scanning device 21, or the side opposite the laser light source.

The application of the illumination device 1 is not particularlylimited; for example, the illumination device 1 can be installed on avehicle, a flying object such as an airplane, a train, a ship, asubmarine, or other moving object. The illumination device 1 can also beplaced at any particular position on those objects.

The invention is not limited to the foregoing embodiments, but allowsvarious modifications that could be conceived by those skilled in theart. Further, the advantageous effects of the invention are not limitedto those described above. In other words, some components can be added,modified, or partially removed without departing from the scope orconcept of the invention defined in the appended claims or derived fromits equivalents.

REFERENCE SIGNS LIST

-   1: Illumination device-   11: Laser light source-   12: Beam expander-   13: Collimating optical system-   14: Light diffuser-   15: Diffusing element-   16: First relay lens-   17: Second relay lens-   18: Relay optical system-   19: Irradiation surface-   20: Scan drive unit-   21: Light scanning device-   22: Controller-   25: Light emission timing control unit-   26: Optical scan control unit-   31: Virtual micro-lens array-   40: Illumination area-   41: Illumination subarea-   45: Reflective mirror-   48: Optical fiber-   50: Optical guide unit-   51: First optical guide member-   52: Second optical guide member-   60: Spectroscopic unit-   61: First spectroscopic guide member-   62: Second spectroscopic guide member-   L: Laser beam

The invention claimed is:
 1. An illumination device comprising: acoherent light source which emits coherent light; a light scanningdevice which changes a propagation direction of the coherent light fromthe coherent light source; and a light diffuser which diffuses thecoherent light from the light scanning device, wherein the lightscanning device scans the coherent light having passed through the lightdiffuser in an illumination area so as to direct the coherent light toillumination subareas constituting parts of the illumination area, thecoherent light which is changed in the propagation direction by thelight scanning device has light components having mutually differentwavelengths, a spectroscopic unit is provided between the light scanningdevice and the light diffuser, the coherent light from the lightscanning device is incident on the light diffuser via the spectroscopicunit, and the spectroscopic unit splits the coherent light from thelight scanning device to separate the coherent light into lightcomponents having mutually different wavelengths and emits the lightcomponents toward the light diffuser.
 2. The illumination device asdefined in claim 1, wherein the spectroscopic unit includes: a firstoptical guide which lets pass therethrough a light component having afirst wavelength range to direct the light component to the lightdiffuser, while reflecting the light components having other wavelengthranges; and a second optical guide which directs the light components ofthe other wavelength ranges reflected by the first optical guide to thelight diffuser.